橋梁結構受沖刷後之耐震行為研究

The Study on Seismic Behavior of Scoured Bridge with Pile Foundation

王修駿(Shiou-Chun Wang)

指導教授 ： 張國鎮

國立臺灣大學/工學院/土木工程學研究所/博士(2014年)

https://doi.org/10.6342/NTU.2014.02056

摘要

本論文探討橋梁結構受沖刷後，其基礎裸露時之耐震行為與土壤結構互制效應。本試驗使用大型剪力試驗盒，建構單柱式橋梁模型，進行基礎裸露之振動台實驗。試驗用橋梁模型，其結構元件分為基樁、基礎板、橋柱與模擬上部結構之質量塊。將樁基礎埋置於乾性土壤與飽和土壤中，樁底固定於剪力盒底部以模擬樁基礎貫入岩盤中之情形。實驗輸入的振動模式為單向振動，包含白雜訊、正弦波加速度與代表性的地震記錄。
並以振動台實驗為基礎，採用有限元素軟體ANSYS建構三維分析模型。土壤的動態性質，並考量樁土界面間的非線性行為，以等效線性方式模擬。經由振動台實驗比對，校驗分析模型之正確性。探討不同的基礎裸露深度對橋梁耐震性能之影響。對於土壤-橋梁-基礎互制系統在地震下的動態歷時反應，提出分析流程。
研究結果顯示，伴隨基樁裸露深度的增加，樁身的彎矩需求將會提高，而橋柱的彎矩需求將會降低，此種轉換機制可能會導致橋梁的破壞模式由橋柱移至樁身，亦可能低估樁基礎在沖刷裸露後的耐震需求。當評估土壤結構互制下的系統阻尼比，其土壤所貢獻的黏滯阻尼，並不會使整體系統的反應產生顯著的改變。

關鍵字

沖刷效應 ； 耐震性能 ； 土壤結構互制 ； 多重災害 ； 振動台實驗 ； 有限元素法

並列摘要

This dissertation presents a study on the seismic performance and soil-structure interaction (SSI) of a scoured bridge models with pile foundation by shaking table tests using a laminar shear box. The model bridge with pile foundation comprised a lumped mass representing the superstructure, a steel pier, and a footing supported by a single aluminum pile within dry soil and saturated soil. The end of the pile was fixed at the bottom of the shear box to simulate the scenario that the pile was embedded in a firm stratum of rock. The model bridge was subjected to one directional shakes, including white noise, sinusoidal accelerations and earthquake ground motions.
A three-dimensional finite element model was created using the ANSYS program to simulate the shaking table tests. The soil dynamic property was taken into consideration for the nonlinearity of the soil-pile interface, and an equivalent linear model was used to capture the soil behavior. The computational model was validated by comparing the results of the finite element analyses with the data obtained from the shaking table tests. The performance of the model bridge with pile foundation was discussed for different scoured conditions. A numerical modeling procedure has been proposed to evaluate the time history response for the seismic behavior of the soil-bridge-foundation interaction system under earthquake excitations.
It is found that the moment demand of pile increases with the increase of scoured depth, whereas the moment demand of the bridge pier decreases, and this transition may induce the transformation of bridge failure mechanism from pier to pile. Thus, the seismic demand on scoured pile foundations may be underestimated and misinterpreted to a certain degree. When evaluating the system damping ratio with SSI, the system response may not be significantly changed even if the soil viscous damping contribution is varied.

並列關鍵字

scour effect ； seismic performance ； soil-structure interaction ； multi-hazard ； shaking table ； finite element method

參考文獻

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